The present invention relates generally to a manner by which to detect a symbol sequence, such as a preamble portion of a data frame, generated during operation of the communication system. More particularly, the present invention relates to apparatus, and an associated method, by which phase calculations are performed to, at least in part, detect receipt at a receiving station of the symbol sequence. Greater detection reliability is provided through operation of an embodiment of the present invention as false, i.e., erroneous, symbol sequence detections are less likely to be made when phase calculations are used to detect the symbol sequence.
Advancements in communication technologies have permitted the introduction, and popularization, of new types of communication systems. In various of such new types of communication systems, the rate of data transmission and the corresponding amount of data to be permitted to be communicated, has increased relative to existing types of communication systems.
New types of radio communication systems are exemplary of communication systems made possible as a result of advancements in communication technologies. Communication channels of a radio communication system are formed upon radio-links, thereby obviating the need for conventional wireline connections between sending and receiving stations operable therein. A radio communication system, therefore, inherently permits increased communication mobility in contrast to conventional wireline systems.
Bandwidth limitations sometimes limit the communication capacity of the communication system. That is to say, the bandwidth capacity of the communication channel, or channels, available to a communication system to communicate information between sending and receiving stations is sometimes limited. And, the limited capacity of the communication channel, or channels, limits increase of the communication capacity of the communication system. The communication capacity of a radio communication system is particularly susceptible to capacity limitations resulting from communication channel bandwidth limitations. Generally, a radio communication system is allocated a limited portion of the electromagnetic spectrum upon which to define communication channels. Communication capacity increase of a radio communication system is, therefore, sometimes limited by such allocation. Increase of the communication capacity of the radio communication system, therefore, is sometimes only possible if the efficiency by which the allocated spectrum is used is increased.
Digital communication techniques provide a manner by which the bandwidth efficiency of communications in the communication system may be increased. Because of the particular need in a radio communication system to efficiently utilize the spectrum allocated in such a system, the use of digital communication techniques is particularly advantageously implemented therein.
When digital communication techniques are used, information which is to be communicated is digitized. In one technique, the digitized information is formatted into packets, or frames, and the packets are communicated to effectuate the communication. Individual ones, or groups, of the packets of data can be communicated at discrete intervals, and, once communicated, concatenated together to recreate the informational content contained therein.
Because packets of data can be communicated at the discrete intervals, a communication channel need not be dedicated solely for the communication of packet data generated by one sending station to one receiving station as conventionally required in circuit-switched communications. Instead, a single channel can be shared amongst a plurality of different sending and receiving station-pairs. Because a single channel can be utilized to effectuate communications by the plurality of pairs of communication stations, improved communication capacity is possible.
Packet data communications are effectuated, for instance, in conventional LANs (local area networks). Wireless networks, operable in manners analogous to wired LANs, have also been developed and are utilized to communicate packets of data over a radio-link thereby to effectuate communications between a sending and receiving station.
For example, A High Performance Radio Local Area Network, type 2 (HIPERLAN/2) standard promulgated by the ETSI sets forth a standard for operation of a wireless LAN operable in the five GHz range. In this standard, a medium access control (MAC) frame structure is defined. The MAC frame structure consists of several kinds of transport channels that are used to deliver both control information and user data. In the system defined by the HIPERLAN/2 standard, as well as other wireless LANs, mobile stations are utilized by users of the network to effectuate telephonic communications. The telephonic communications include, for example, voice as well as data communications.
Data which is to be communicated is formatted into frames of data in which a frame is formed of a preamble portion and a payload portion. Frame-formatted data is transmitted, for instance, on the down-link transport channel. A mobile station tuned to a frequency channel must be able to detect the preamble portion of the frame so that the informational content of the frame, i.e., the payload portion, can be properly utilized.
In at least one existing manner proposed by which to detect the preamble portion, correlation calculations are performed by the mobile station. A ratio is formed of the calculated correlation value relative to average power levels. And, the ratio, so-formed, is compared with a threshold value. If the value of the ratio is greater than the threshold, a determination is made that the preamble portion of the frame is received, and following portions of the frame form the payload.
However, performing such calculations on other portions of the frame might also indicate that such other portions of the frame form the preamble portion. Therefore, the reliability of this existing manner by which to detect the preamble portion is deficient.
A manner by which more reliably to detect reception of a preamble portion of a frame of data would therefore be advantageous.
It is in light of this background information related to the communication of data that the significant improvements of the present invention have evolved.
The present invention, accordingly, advantageously provides apparatus, and an associated method, by which to detect, at a receiving station, reception of a selected symbol sequence, such as a preamble portion of a frame of data. Phase calculations are performed to detect, at least in part, the selected symbol sequence.
Operation of an embodiment of the present invention provides a manner by which to detect the selected symbol sequence with greater reliability than generally possible through the use of conventional detection techniques. Particularly when phase calculations, performed pursuant to the operation of an embodiment of the present invention, are used together with correlation and power level calculations, false, i.e., erroneous symbol sequence detections are less likely to be made, thereby resulting in improved performance of the receiving station at which an embodiment of the present invention is operable.
Also, ratio calculation of calculated correlation values relative to calculated power level values is a computationally-intensive procedure. Through operation of an embodiment of the present invention, such ratio calculation is performed only if the phase calculation indicates detection of the selected symbol sequence.
In one aspect of the present invention, a receiving station is tunable to receive frame-formatted data transmitted thereto upon a communication channel. Each frame of the frame-formatted data is formed of a preamble portion and a payload portion. The selected symbol sequence detected during operation of an embodiment of the present invention is the preamble portion of a frame of data. Phase calculations are performed upon successive sequential portions of the symbols received thereat. If the calculated phase values exceed a phase-value threshold level, at least a preliminary determination is made that the corresponding symbol sequence forms the preamble portion of a frame. In the exemplary implementation, subsequent to detection of the calculated phase value to be in excess of the phase-value threshold, a further comparison is made prior to final determination that the corresponding symbol sequence forms the preamble portion of a frame of data. In this implementation, a peak test is further performed. That is, a determination is made as to whether a ratio formed of correlation values of the sequence relative to average power levels of the sequence are beyond a peak-value threshold. If so, a final determination is made that the corresponding symbol sequence is the preamble portion of the frame of data. Thereafter, processing can be performed upon the payload portion of the frame. Also, in one implementation, timing synchronization is performed to synchronize the receiving station with the signal received thereat.
In another aspect of the present invention, a mobile station is provided for a wireless LAN (local area network) such as that defined in the ETSI-promulgated HIPERLAN/2 standard for a five GHz, wireless LAN. In the system defined therein, a TDD (time division duplex) communication scheme is utilized. Frames of data are broadcast by network infrastructure, such as by an access point which forms a portion of the network infrastructure. Frames of data are broadcast, for instance, upon a system specific transport channel for control information, BCH. And, mobile stations are tunable to a frequency channel to receive the frames of data broadcast thereon. Each frame is formed of a preamble portion and a payload portion. And, in order to determine properly the content of the payload portion of the frames of data, the mobile station must first detect the preamble portion of a frame. An embodiment of the present invention is operable at a mobile station operable in such a HIPERLAN/2 system. Computations are made upon successive portions of data, broadcast upon the BCH and received at the mobile station. The computations include calculation of correlation values of successive, sequential portions of the receive signal and also calculations of corresponding average power levels. The calculated correlation values are utilized to calculate phase values of the corresponding segments. A determination is made whether the calculated phase values exceed a phase-value threshold level or at least a selected period. If not, a determination is made that the corresponding sequence is not the preamble portion of a frame of data. If, however, the calculated phase values exceed the phase-value threshold, an additional peak test is performed. The peak test determines whether a ratio formed of the calculated correlation values relative to the calculated average power levels exceed a peak-test threshold. If so, a determination is made that the corresponding sequential portion of the receive signal forms the preamble portion of a frame of data. Such a determination permits additional operations to be performed upon the data payload of the frame and also to permit time synchronization between the mobile station and the network infrastructure from which the forms of data are broadcast upon the BCH.
In the aforementioned HIPERLAN/2 system, the preamble portions of the frames of data broadcast upon the BCH by the network infrastructure are of values which exhibit two correlation peaks and a phase value of xcfx80 radians around the first correlation peak. Calculations performed at the mobile station detect both the phase peak and the correlation peak so that reception of the preamble portion of a frame of data is detectable at the mobile station. In other implementations, other peak and phase locations are otherwise determinable to detect the preamble portion of a corresponding frame of data.
In these and other aspects, therefore, apparatus, and an associated method, is provided for a communication device operable at least to receive a data sequence generated during operation of a communication system. The data sequence includes a selected symbol set which identifies a start of the data sequence. Detection is made during operation of an embodiment of the present invention of the selected symbol set. A phase detector is coupled to receive indications of the data sequence once received at the communication device. The phase detector detects phase values associated with successive portions of the data sequence. And, a selected symbol set detector is coupled to receive indications of the phase values detected by the phase detector. The selected symbol set detector is operable, at least in part, responsive to the indications of the phase values to detect reception of the selected symbol set.
A more complete appreciation of the present invention and the scope thereof can be obtained from the accompanying drawings which are briefly summarized below, the following detailed description of the presently-preferred embodiments of the invention, and the appended claims.